The invention relates to an assembly of a belt retractor for a vehicle safety belt and of a force limiter.
An assembly of a belt retractor for a vehicle safety belt and of a force limiter, the belt retractor having a belt spool and the force limiter having a housing and a driving part which is able to be coupled with the belt spool, is known from German Utility Model 298 16 280. The force limiter serves to make possible a rotation of the belt spool of the belt retractor in the belt webbing unwinding direction contrary to a predetermined moment of rotation, so that belt webbing can be withdrawn from the belt spool, which is available as an additional way to decelerate a vehicle occupant. In this way, force peaks in the vehicle safety belt can be reduced, so that the risk of injury for a vehicle occupant who is to be restrained is lowered.
Generally, in belt retractors which are provided with a force limiter, the problem exists that after a primary impact, in which the force limiting function became effective, it is not desired for further belt webbing to be able to be withdrawn from the belt spool. If further belt webbing were able to be withdrawn from the belt spool, the vehicle occupant could move further forward in a secondary impact following the primary impact. Such a further forward movement could lead for example to the vehicle occupant coming into contact with for example a vehicle steering wheel or with a part of the instrument panel, because the gas bags which are usually used today, after they have become effective in a primary impact, do not provide a sufficient restraining effect for a secondary impact.
Therefore, the problem of the invention consists in further developing an assembly of the type initially mentioned to the effect that after a primary impact, the belt spool is reliably locked so that no further belt webbing can be withdrawn therefrom.
The invention provides an assembly comprising a belt retractor for a vehicle safety belt and a force limiter. The belt retractor comprises a belt spool, and the force limiter comprises a housing and a driving part able to be coupled with the belt spool. The assembly comprises a locking catch connected with the driving part, a release mechanism for the locking catch, and a stationary locking toothing into which the locking catch can be caused to engage by the release mechanism. The release mechanism is able to be activated by a relative rotation between the driving part and the housing of the force limiter and, towards an end of this relative rotation, can cause to engage the locking catch into the locking toothing whereby the belt spool is locked against a rotation in a belt webbing withdrawal direction relative to the locking toothing. The process of force limitation, i.e. the withdrawal of belt webbing from the belt spool contrary to a resistance torque, is substantially unchanged in the assembly of the invention compared with the prior art. The release mechanism is in fact activated by the beginning of the force limiting function; the locking catch, however, remains up to the conclusion of the force limiting function in its position in which it does not engage into the locking toothing. Only with the termination of the force limiting function, i.e. when the driving part has come to rest relative to the housing of the force limiter, is the locking catch engaged into the locking toothing, so that no further withdrawal of the belt webbing from the belt spool is possible. Therefore, it is ensured that also in the case of a secondary impact a restraining effect can be provided for the vehicle occupant, no further force limiting function being effective then, however. The disconnection of the force limiting function therefore not only ensures that in the case of a secondary crash only a small forward movement of the vehicle occupant is possible; in addition, advantages occur in the design of the belt retractor and in particular of the force limiter. The force limiter only has to be designed so that it makes possible in a primary impact the withdrawal of the necessary length of belt webbing (approximately 300 mm belt webbing). As in a secondary impact the belt webbing is directly locked and no further force limiting function is effective, the force limiter does not need to be designed so that it also makes possible in addition a withdrawal of belt webbing in this case.
According to a preferred embodiment, provision is made that the locking toothing is arranged on the housing of the force limiter. This results in a particularly compact construction.
According to the preferred embodiment, provision is further made that a locking catch is arranged on the belt spool, which locking catch can be caused to engage into the locking toothing arranged on the driving part, so that the belt spool is coupled with the driving part. This construction makes it possible in a particularly simple manner to use a conventional belt retractor, as is described for example in the German Utility Model 298 12 435, to which reference is made expressly here, in connection with a force limiter as is known from the utility model initially mentioned. The locking catch, which usually serves to lock the belt spool by engagement into a toothing fixed to the frame, now serves to couple the belt spool with the force limiter. When the locking catch is not activated, the belt spool can rotate freely. This corresponds to the usual operation. If, on the other hand, the locking of the belt spool is activated, for example because the acceleration or deceleration of the vehicle exceeds a particular threshold value or the rotational acceleration, acting on the belt spool and brought about by high belt webbing forces, exceeds a particular threshold value, the belt spool is connected with the force limiter via the locking catch. As the force limiter only becomes active on exceeding a predetermined moment of rotation and makes possible a rotation of the driving part relative to the housing, the locking toothing arranged on the driving part acts like a toothing fixed to the housing as long as the moment of rotation applied onto the driving part remains below the value after which the force limiter is active. If, in this state, the moment of rotation acting on the belt spool falls again, the locking catch is released again from the locking toothing and the belt spool can rotate freely. If, on the other hand, the acting moment of rotation exceeds the threshold after which the force limiter is active, a relative rotation is brought about between the driving part of the force limiter and its housing, so that belt webbing from the belt spool is possible contrary to the resistance torque provided by the force limiter.
According to a preferred embodiment of the invention, the release mechanism is arranged on the driving part. In this way, the relative rotation used for activation of the release mechanism can be detected immediately between the driving part and the housing.
Preferably, provision is further made that the locking catch is mounted on the driving part. This provides a very compact construction and a direct transfer of force without detours.
According to a first embodiment, the release mechanism comprises a cage which is rotatable relative to the driving part from an initial position in which the locking catch does not engage into the locking toothing, into an activated position in which the locking catch is caused to engage into the locking toothing. In this way, a particularly compact construction is produced, in particular when the release mechanism comprises a spring which biases the cage from the initial position into the activated position, and when the locking catch is mounted on the driving part. Furthermore, provision can be made that the locking catch is provided with a nose which co-operates with a ramp constructed on the driving part, so that the locking catch, on a rotation of the cage, is caused to engage from the initial position into the position of rest into the locking toothing.
According to the first embodiment, in addition a holding pin is provided, which can hold the release mechanism in the initial position and engages into a mounting in the housing of the force limiter, so that it is sheared off with a relative rotation between the driving part and the housing of the force limiter, whereby the release mechanism is activated. This construction makes it possible in a particularly simple manner to use an occurring relative rotation between the driving part and the housing for activation of the release mechanism.
According to a second embodiment, the locking catch is arranged on a slider, the mass and geometry of which are selected such that the overall mass center of locking catch and slider lies on the side of the rotation axis of the driving part facing away from the locking catch. Deviating from the first embodiment, in which the release mechanism responds substantially as a function of the acceleration values, in this construction the locking catch is actuated as a function of the rotational speed. When the rotational speed is so high that the centrifugal force generated by the overall mass center is greater than the effect of the spring, which attempts to guide the locking catch into the locking toothing, the locking catch is kept at a distance from the locking toothing. As soon as the rotational speed falls below a particular value, the force exerted by the spring exceeds the centrifugal force, so that the locking catch is caused to engage into the locking toothing.
Preferably, in addition, a holding pin is provided, which is arranged on the housing and is elastic, a nose being arranged on the locking catch, against which the holding pin can lie and the locking catch can be kept, contrary to the force exerted by the spring, in the position not engaged into the locking toothing. The holding pin can therefore yield elastically, so that it is not obstructive in the case of a relative rotation between the driving part and the housing. Preferably, a slope is provided on the housing, which slope adjoins the nose of the locking catch and deflects the holding pin outwards when the driving part is rotated relative to the housing. As the holding pin is no longer sheared off, it does not represent a loose part which after activation of the force limiting function could have an intrusive effect inside the housing.
In the second embodiment, provision can be further made that a holding surface is constructed on the housing and a projection is constructed on the locking catch, the projection engaging behind the holding surface when the locking catch is situated in its position not engaged into the locking toothing. The holding surface together with the projection acts in the same direction as the holding pin engaging on the nose, i.e. contrary to the action of the spring. In this way, the action of the spring is compensated in a phase of the relative rotation between the driving part and the housing in which the rotational speed of the driving part is still comparatively low, so that the centrifugal force generated by the overall mass center is likewise comparatively low.
Advantageous developments of the invention will be apparent from the sub-claims.